Phantoms are routinely used for performance testing and quality assurance of nuclear imaging systems. Certain complex phantoms are used to simulate realistic patient imaging systems and diagnostic tasks, such as lesion detection. However, existing designs for such phantoms have limited accuracy and reproducibility, and they are particularly inconvenient to use. These limitations have restricted the widespread use of such phantoms to research studies. In Phase I, we have produced a prototype innovative phantom for testing lesion conspicuity, whose design overcomes the above limitations. We have evaluated the performance of this phantom in nuclear medicine scanners. We have found that this phantom produced images with the expected lesion-to-background contrast ratio and with excellent uniformity, and it was much easier to prepare than existing designs for such phantoms. In Phase II, we will complete the development of a commercial-quality version of the phantom. We will also develop phantoms based on this novel design for evaluating attenuation correction and for simulating anthropomorphic structures. This research will lead to commercial products that will be very valuable for routine quality assurance, for clinically relevant performance comparisons between scanners, and for research studies. PROPOSED COMMERCIAL APPLICATION: This research will lead to commercial phantoms for nuclear medicine imaging that are more accurate, reproducible, and convenient to use than existing phantoms. The phantoms will be used for acceptance testing, quality assurance, performance comparisons, and research for SPECT and PET scanners.